Metabolism

"The human body uses carbohydrate, fat and protein in food and from body stores as energy. These essential nutrients are needed regardless of the intensity of activity you are doing. However, in order for these nutrients to be used as fuel for the body, their energy must be transferred into the high-energy molecule known as adenosine triphosphate (ATP). ATP is the body’s immediate fuel source of energy that can be generated either with the presence of oxygen, known as aerobic metabolism, or without the presence of oxygen, by anaerobic metabolism. The type of metabolism that is predominantly used during physical activity is determined by the availability of oxygen and how much carbohydrate, fat, and protein are used.\n\nAnaerobic metabolism occurs in the cytosol of the muscle cells. A small amount of ATP is produced in the cytosol without the presence of oxygen. Anaerobic metabolism uses glucose as its only source of fuel and produces pyruvate and lactic acid. Pyruvate can then be used as fuel for aerobic metabolism. Aerobic metabolism takes place in the mitochondria of the cell and is able to use carbohydrates, protein, or fat as its fuel source. Aerobic metabolism is a much slower process than anaerobic metabolism but produces the majority of the ATP."